Containers with pressure control devices are known in patent literature since almost thirty years but until today no commercial products are available on the market.
In EP-A-0 349 053 a pressure capsule for a spray can is described, which consists of two chambers. The first chamber is filled with a fluid under relatively high pressure and the second chamber is filled with a fluid with a pressure equal to the overpressure which normally exists in the spray can and needed for expelling a liquid. In the wall of the second chamber a membrane controls a valve. A plug in the wall keeps the fluid under pressure so that the valve keeps closed.
In WO-A-93/22222 (Cruysberghs) published in 1993 a pressure control device for maintaining a constant pressure in a container is disclosed in principle. Many different embodiments of the device are described, but in practice none was realized in commercial scale.
Another example of such a pressure control device is known from PCT patent application WO-A-99/62791. The device described therein is provided for maintaining a constant predetermined pressure in a container which is arranged for dispensing a fluid. The pressure control device has a first chamber and a second chamber, as well as a closing member movable relative to the second chamber for releasing and closing a fluid connection between the first chamber and the container depending on the position of the closing member relative to the second chamber. The first chamber is filled with a gas which, in use, has a higher pressure than the pressure in the container. The second chamber is closed having a gas at a predetermined or reference pressure and is located outside the first chamber. In a first embodiment according to FIG. 2 of WO-A-99/62791, the first chamber is provided as a cup-shaped holder which is placed upside down in the container and has its longitudinal edge joined together with the bottom and the upright sidewall of the vessel or container. In FIG. 3a second embodiment is shown in which the diameter of cup-like first chamber is much smaller than the inner diameter of the container. The chamber is centrally disposed within the container and joined at its longitudinal edge with the bottom of the container. In FIG. 4a third embodiment is shown in which the same first chamber as in FIG. 3 is disposed eccentrically with respect to the container. In FIG. 5a disc is provided slightly below the middle of the height of the vessel and is gas-tightly connected with the inner wall of the vessel through a sealing ring. This disc divides the vessel into two (fixed arranged) parts. A similar construction is shown in FIGS. 6a and 6b. Further, in FIG. 7 the first chamber of pressure control device is designed as a plunger which is sealed to the inner wall of the container with a sealing ring and which can be moved in axial direction within the container. Thus, the plunger divides the container in two parts, wherein the upper part is filled with the fluid to be dispensed. The fluid connection from the first chamber terminates in the lower part. When the pressure in the container drops since fluid has been dispensed by the push button on top of the container, the plunger is moved upwards because of the pressure difference between the lower and the upper part until pressure equilibrium between the lower and the upper part is obtained again. Therefore, the pressure in the lower part has decreased so that the pressure in the second chamber will be higher and the closing member will open the fluid connection between the first chamber and the lower part, so that the pressure in the lower part will rise. The plunger will then be moved upwards again until a pressure equilibrium is achieved corresponding to the predetermined or reference pressure in the second chamber. Finally, in the embodiment according to FIG. 8 the first chamber is of cylindrical design and has an outer diameter corresponding to the inner diameter of the container and thus fitted tightly within the container.
Only the pressure device of FIG. 7 of WO-A-99/62791 is movable in an axial direction. In all other examples the pressure device is fixedly arranged within the container. The complete pressure control device of FIG. 7 is designed as a plunger which functions as a movable piston expelling the dispensing fluid. However, the design of the pressure control device is disadvantageous because of its large dimensions so that less of the container can be used for dispensing fluid.
A further important problem of the above described pressure control devices as a separate module is that the first and second chambers have to be pressurized before mounting in a container. This in practice may be very difficult and costly to achieve e.g. in aluminium aerosol cans where the construction is in one-piece and the production lines run at very high outputs. A further major disadvantage is that it has been shown that the pressure in a separate pressure control device which will be mounted afterwards in a container drops to a large extent during a period of some months which is necessary for storage and distribution in the commercial supply chain. In addition, pressurizing of the pressure control device has to be performed with the fluid connection closed in order to obtain a pressure of the prescribed quantity. Thus the known pressure control devices are not suitable for application in a large industrial scale.
It is therefore an object of the present invention to provide a pressure control device for a fluid dispensing container which is simpler in construction. Another object of the invention is to provide a manufacturing process of the pressure control device which may be assembled easily in a fluid dispensing container.